Orthodontists are principally concerned with the straightening of irregular or "mal-occluded" teeth. Generally the corrective technique first involves diagnosing the extent of the mal-occlusion and devising a course of treatment in which teeth are repositioned into a desired configuration. The desired configuration of the teeth in the dental arches, traditionally, has had the following characteristics:
1. The occlusal (biting) surfaces of the crowns of the teeth in the upper and lower dental arches meet in a relatively flat "occlusal" plane; and PA1 2. The cusps of the crowns in one arch interdigitate with the cusps of the crowns of the opposing arch in a prescribed manner. PA1 (a) better assess the mal-occlusion; PA1 (b) formulate a treatment plan including proper root dispersion; PA1 (c) orient the precision slot of an orthodontic bracket to the crown and root of each tooth; PA1 (d) design proper force systems (moment to force ratio) to control movement of the tooth roots as well as the crowns; and PA1 (e) evaluate the efficiency of the force systems and assess crown and root movement throughout the orthodontic treatment period.
In recent years the position of the tooth roots in the bone has become an important added characteristic of the desired configuration of the teeth at the completion of orthodontic treatment. This characteristic is stated as "proper dispersion of the roots in the supporting medium (bone)".
To obtain these characteristics of the desired configuration of the dental arches and in particular, "the proper dispersion of the roots in the supporting medium", certain information is essential. Further, the accuracy of this information can improve the level of treatment.
The knowledge of the root position of each tooth which is buried in the supporting bone is of paramount importance for orthodontic treatment from early diagnosis of the mal-occlusion and throughout the treatment period to its conclusion.
Thus, if the orthodontist knows the precise position of the roots, he or she is able to:
Once the diagnosis and treatment plan has been formulated, the orthodontist attaches orthodontic brackets (braces) on the crowns of the patient's teeth. The accuracy of properly orthodontic bracket placement on the crowns of the teeth is considered by the orthodontist as the most important procedure in all of treatment. This is because the orthodontic bracket which is usually made of metal, has a precision slot that must be oriented properly to the long axis of the tooth. This precision slot is some 2-4 mm in length and rectangular in cross-section to receive an "arch wire". An arch wire is a length of springy, small diameter wire that the orthodontist shapes around the dental arch from crown to crown to be received by the precision slot of each bracket on the crown of each tooth.
Initially small diameter arch wires are placed--wires that fit loosely in the precision bracket slots. As the bracket slots begin to line up, one to another, larger diameter arch wires can be placed. Ideally, a full size arch wire (one whose cross-section totally fills the precision bracket slot) can eventually be placed in all the bracket slots for all the teeth in one arch. Because the precision slot of the bracket and the larger arch wire are the same size and rectangular shape in cross section, the arch wire can control the bracket in all planes of space.
The bracket is attached to the crown of the tooth and each crown has an attached root, thus the arch wire controls the crown and root of each tooth in all planes of space. The relationship of the attachment of the crown to the root is constant and is not altered during orthodontic treatment.
Therefore, if the slot of each bracket could be oriented properly to the crown and root of each tooth and so attached to the crown of each tooth, a full size flat rectangular arch wire placed in each bracket slot would properly position all the crowns in relation to each other and, in addition, would properly disperse all the roots.
Generally, one of two methods is used to place brackets on the patient's teeth to accept the spring arch wires. These are the direct and the indirect methods.
The direct method involves fixing of the arch wire brackets to the teeth directly in the patient's mouth. The orthodontist attempts to center the bracket in a mesial-distal direction plus orient the precision slot to the crown's long axis. The crowns of teeth in a mal-occlusion are in disarray and thus it is frustrating for the orthodontist who must guess at proper bracket placement while controlling lips, tongue and saliva of the patient.
This must be done without accurate knowledge of the crown to root orientation. Further, in the direct method this must be accomplished by visual observation and hand manipulation and inaccuracy of bracket placement is a reality. Inaccurately placed brackets create difficulties in properly adapting arch wires and calculating the force requirements for correcting mal-aligned teeth. In addition, the precision slot of the bracket will not indicate to the orthodontist the position of the tooth root in the surrounding bone. This makes it even more difficult for the orthodontist to analyze and plan a course of corrective development through a period of time.
The indirect method involves initial bracket placement away from the patient in a laboratory atmosphere. In its most rudimentary form, the indirect method involves the same bracket placement procedures used in the direct method with the only difference being that the brackets are first attached to a cast model of the mal-occlusion. They are then removed from the model and placed on the patient's teeth. This process has proven to be more effective than the direct method but is not at all without its own unique difficulties.
To solve some of these difficulties of the indirect method an ideal "set-up" can be done: A "set-up" is a procedure where the individual crowns plus 4-5 mm of the gum tissue area below each crown is cut free of the base of the mal-occlusion cast. Thus, each tooth model consists of a tooth crown and a long section of the gum area directly below the tooth.
The individual tooth models may then be reassembled on a wax rim shaped like a dental arch in an "ideal" arch configuration. To make any change of a tooth position, a spatula is heated and then inserted into the wax around the tooth to be altered. This procedure is tedious, lacks precision in altering tooth positions and, even more importantly, no root structure can ever be evaluated as a part of the set-up method. Only the crowns and some of the gingival (gum) tissue is available for observation. Thus the orthodontist or technician must guess at the long tooth axis to determine proper tooth alignment in the "ideal" set-up. The resulting "ideal" set-up is therefore far from "ideal". It is often an unrealistic, unobtainable set-up because the changes of root angles from the mal-occlusion to the set-up are not coordinated as orthodontically feasible.
Previous indirect methods have made use of the wax base to hold the tooth crown models from the gingival areas of the tooth models while the orthodontist or lab person tries to position the crown. This method of holding the crown obstructs the area where the root of the tooth is actually located. This adds even further difficulty in accomplishing proper dispersion of the tooth root when the area of the roots are not visible.
In the natural dentition, the joint transition section between the crown of a tooth and its root is not visible. The transition sections are imbedded in alveolar bone (bone that forms the socket for the root of a tooth). In addition, a portion of the crown of a tooth and the alveolar bond around the root is covered by various thicknesses of gum tissues.
The closest observation of the transition section between the crown and the root in nature is produced by X-ray. Because an X-ray takes a three dimensional object and reproduces it in two dimensions, accuracy is greatly diminished. This is especially true in mal-occlusions where the third dimension (depth) may be very irregular. Some dimensional input can be obtained, however, by making use of a number of X-rays taken at different recorded angles. However, this is not a practical approach nor is extensive radiation of the patient justifiable. However, to reiterate, knowing the location of the roots in all planes of space is essential for quality orthodontic treatment at the beginning, during, and at the completion of such treatment. Knowledge of the root location is important for orienting the precision slots of orthodontic brackets to the crowns and roots of the teeth, the designing of force systems to move the teeth, the treatment progress and the final evaluation of the level of success of the treatment.
If proper orientation of the slot of an orthodontic bracket can be obtained in relationship to the long axis of the individual tooth, then for the rest of the treatment period the orthodontist has only to refer to the bracket slot to know where the root is located.
The present applicant, in U.S. Pat. No. 3,922,786, discloses a method and apparatus for forming and fitting orthodontic appliances. This method and apparatus came from the assumption that there is a correlation between the long axis of a tooth and its labial surface. Thus the contour of the backing of the orthodontic bracket would orient the slot to the long axis of the tooth. It is an assumption based on "averages" and is used by orthodontic manufacturers in producing current orthodontic brackets. They imply that placing a full sized arch wire in the precision bracket slots will render an ideal positioning of all tooth. E. L. Dellinger, in an article titled "A Scientific Assessment of the Straight Wire Appliance," American Journal of Orthodontics 73:290-299, 1978, contended that a full sized wire should not be used with an average inclination built into the bracket, otherwise the results may "be erratic, inconsistent and clinically unacceptable." However, practice with this device has indicated that although an "average" root axis angle can be determined by this apparatus and method, it is not sufficiently accurate in all situations. Furthermore, the method and apparatus works in reverse from actual placement of brackets on the patient's teeth. This becomes a very difficult procedure since it is more desirable to know of the root angles prior to bracket placement.
An indirect method for placement of brackets on a patient's teeth is indicated in U.S. Pat. No. 3,439,421 to T. E. Perkowski. Perkowski discloses an orthodontic articulator that permits reassembly of a patient's teeth into a desired form of realignment under an arch plate that is inscribed with a line indicating the arch configuration of the patient's dentition. A bracket positioning gauge is also disclosed for use in conjunction with the articulator for positioning brackets on an "ideal" model comprised of repositioned individual tooth models set-up under the arch plate in a wax base. Thus, individual adjustment of the tooth models is accomplished in the above mentioned manner, using heated spatulas, etc.
The Perkowski bracket placement mechanism involves the use of a base with a flat surface for sliding across a reference table surface. A bracket mounting arm is adjustably positioned on the sliding base with an extending pin positional by the adjustment mechanisms to the desired level at which the various brackets are to be placed on the "ideal set-up". The brackets are received by the pin along their arch wire slots. They will pivot about the axis of the pin as the pin is moved into position to attach the bracket to the model tooth. Therefore, orientation to the bracket slot is not controlled by the mounting arm but rather by the labial surface of the tooth and the bracket backing, which may vary considerably. The tooth curvature may cause the bracket to pivot on the carrying pin to a position wherein vertical wall of the slot is not perpendicular to the desired plane for the arch wire.
U.S. Pat. No. 3,521,355 to Pearlman discloses means for positioning orthodontic brackets. This mechanism is provided primarily for use in conjunction with plastic brackets and their use in the "direct" method of placement within the patient's mouth. The disclosure, however, does indicate the importance of positioning individual brackets in relation to the incisal surfaces of the individual teeth.
U.S. Pat. No. 3,657,817 to Kessling discloses a holder for orthodontic brackets used to provide a gripping surface by which an orthodontist or lab technician may hold individual brackets while they are attached as by spot welding to bracket bands. This patent again indicates the importance or accurate positioning for the brackets in relation to the associated teeth.
U.S. Pat. No. 3,521,354 to A. J. Stern et al discloses a method of assembling dowels in tooth dies. The purpose of the dowel arrangement is to facilitate insertion and removal of individual tooth models in relation to a cast base, without interfering with the dowel pins of adjacent tooth models. The purpose, therefore, is to arrange all the dowel pins in parallel orientation to one another, rather than to indicate the longitudinal root axis of the associated tooth to facilitate proper and accurate bracket placement.
It is valuable to view the individual tooth structure from mesial and distal aspects in order to determine root orientation. In direct placement of brackets on a solid set-up model or by the direct method on the patient's teeth, mesial and distal aspects are hidden by adjacent tooth structures. Therefore, the observer has ability only to view the features of a tooth from the labial, and with some difficulty the lingual aspects to determine root angulation. While this gives a general picture of the root orientation, it is not a precise method for locating the long root axes.
Of the above discussed disclosures, none provide means by which the long axes of the individual teeth may be accurately determined or indicated and recorded. Furthermore, substantial guess-work still remains in the placement procedures and adjustments by which bracket positioning is achieved. It therefore remains desirable to learn of and be able to record the exact location of roots of all the teeth in the mouth and, with such information available, obtaining the capability of accurately and effectively completing orthodontic treatment.
A first object of the present invention is to facilitate reproduction on the laboratory bench of all the crowns of the teeth of a patient's mouth with all the long tooth axes readily accessible.
Another object is to provide an apparatus system and process to initially locate the position of the roots and the manner of attachment in all planes of space that the roots have to their respective crowns.
It is a further object to record the spatial crown-to-root relationships by actually attaching a simulated root to the model of the crown of each tooth.
It is a still further object to make the precise location of any root initially and throughout treatment readily retrievable information by a simple index impression of the crowns which, of course, are visible in the mouth. The model crown with the simulated root attached is placed in the proper crown recess of the index impression. Plaster is poured around the simulated roots rendering a reproduction of the arrangement that the crowns have in the patient's mouth. By removing a little plaster on the labial side of the gum area adjacent to the root areas special features of the simulated root are exposed. These special features provide the needed information about the actual roots for or quality orthodontic treatment.
Another object is to provide an apparatus system by which individual crown models can be surveyed to determine precisely the exact orientation of the long tooth root axis in relation to the incisal, labial, lingual, mesial and distal surfaces of the crown.
A still further object is to provide an apparatus system by which a realistic "ideal" set up model of a patient's teeth can be produced, showing realistically the relative positions of the teeth following orthodontic treatment.
Another object is to provide an apparatus system by which the precision slots of orthodontic brackets can be positioned and recorded in relation to individual crown models of a patient's teeth.
A yet further object is to provide an apparatus and system for determining bracket thickness and backing caricature appropriate for individual crowns.
These and still further objects and advantages of the present invention will become apparent from the following description which, taken with the accompanying drawings, disclose a preferred form of the present invention.